Surgical instruments

ABSTRACT

A kit of parts for inserting a deformable implant into a cavity in a bone of a patient is described. An inserter instrument ( 1 ) comprises a body ( 100 ) having a cavity extending along a longitudinal axis from a distal end to a proximal end. An attachment mechanism ( 108 ) is provided at the distal end and to which a deformable implant can be releasably attached. A drive mechanism ( 132 ) is provided at the proximal end of the body. A push rod ( 150 ) is freely and slidably arranged within the cavity and has a distal end engageable with a part of the deformable implant and a proximal end abutable by the drive mechanism. The drive mechanism is operable to drive the push rod toward the distal end of the body. The kit also includes an impactor ( 210 ) dimensioned for slidable engagement within the cavity.

CROSS REFERENCE TO RELATED APPLICATION

This application is a National Stage 35 U.S.C. 371 of InternationalPatent Application No. PCT/GB2013/051398 filed May 28, 2013 which claimspriority to United Kingdom Patent Application Nos. GB1209809.1, filedJun. 1, 2012 (now abandoned) and GB1304726.1, filed Mar. 15, 2013 (nowabandoned).

The present invention relates to a surgical instrument and in particularto a surgical instrument and kit of parts for inserting an implantcomponent into a cavity in a bone of a patient.

WO 2010/097636 describes a support structure implant and assembly,including an instrument, for deploying such an implant. The handling,insertion, deployment and subsequent use of deformable implants canrequire significant care, for example in order to ensure that theimplant is correctly inserted and/or positioned within the bone cavityand/or does not move within the bone cavity after implantation and as itis being used, or otherwise interacted with, during subsequent surgicalsteps in order to complete the surgical procedure for which the implantis intended.

Therefore instrumentation to increase the reliability and/or ease ofinsertion and/or deployment of deformable implants would beadvantageous.

A first aspect of the invention provides an inserter instrument forinserting a deformable implant into a cavity in a bone of a patient. Theinserter instrument can comprise a body having a cavity extending alonga longitudinal axis of the body from a distal end to a proximal end. Anattachment mechanism can be provided at the distal end, to which adeformable implant can be releasably attached. The inserter instrumentcan include a drive mechanism at the proximal end of the body. Theinserter instrument can further comprise a push rod freely and slidablyarranged within the cavity. A distal end can be engageable with a partof the deformable implant. A proximal end can be abutable by the drivemechanism. The drive mechanism is operable to drive the push rod towardthe distal end of the body.

The instrument uses a freely sliding push rod actuable by a drivemechanism which can abut against a free end of the push rod and hencehas a particularly simple construction which facilitates assembly, use,disassembly, cleaning and ease of manufacture of the instrument.

A part of the drive mechanism can be removable from the instrument. Thepush rod can be slideably removable from the instrument via the proximalend of the body. Hence, the push rod can be removed from the instrumentwhile the instrument is still attached to the implant. Hence, the bodycan be used for a secondary purpose, such as the transfer of bone graftto the implant, without interfering with the placement of the implant.

The push rod can have a longitudinal length greater than a longitudinallength of the cavity of the body. Preferably the longitudinal length ofthe push rod is at least the length of the cavity and the length of roddeformable implant in the direction of the longitudinal axis. Preferablythe longitudinal length of the push rod is at least the length of thecavity and the length of rod deformable implant in its maximallydeformed state in the direction of the longitudinal axis. Morepreferably the longitudinal length of the push rod is greater than thelength of the cavity and the length of rod deformable implant in itsmaximally deformed state in the direction of the longitudinal axis.

The length of the push rod can be greater than the length of the cavityand the length of the implant in the direction of the longitudinal axis(in either the deployed or the deformed state) such that a portion ofthe push rod is proud of the proximal end of the body and hence easilyabutable by a part of the drive mechanism.

The drive mechanism can include a pair of matching threads and a surfaceabutable against the proximal end of the push rod and caused totranslate along the longitudinal axis by the threads. The drivemechanism can include an internal thread and an external threadco-operating with the internal thread. The drive mechanism can include acap. A part of the cap, such as an inner surface, can be arranged toabut the proximal end of the push rod. The cap can includes a one of theinternal thread and the external thread. The proximal end of the bodycan include the other of the internal thread and the external.

The external thread can be provided on an outer surface of the body atthe proximal end of the body. The internal thread can be provided on aninner surface of the cap.

The cap can include a grip formation disposed on an outer surface aroundits periphery providing a grip for rotation of the cap about thelongitudinal axis by a user.

The cap can be in the form of a rotatable knob.

The inserter instrument can further comprise a stop arranged to limitthe extent of travel of the push rod within the body toward the distalend. The stop can comprise a member extending from the push rod. Thestop can further comprise a channel in an inner wall of the body andhaving an end wall. The member can be arranged to slide within thechannel and to abut against the end wall. The member and channel canfurther co-operate to prevent rotation of the push rod about thelongitudinal axis. The stop can further be arranged to prevent bindingof the drive mechanism.

The inserter instrument can further comprise a hopper. The hopper can beattached to an upper surface of the body. The hopper can include a loweropening in communication with the cavity.

The inserter instrument can further comprise a discontinuity in itsouter surface. The discontinuity can provide a vent in use to prevent orreduce any increase or decrease in pressure within the bone. Thediscontinuity can be in the form of a flat surface and the flat surfacecan be on an upper part of the instrument. The discontinuity can extendalong the instrument body and can extend for at least a quarter, a half,two thirds or three quarters of the length of the body. Thediscontinuity can extend to the distal end of the body. Thediscontinuity can extend from the distal end of the body to a scale onthe body or to a stop on the body or to a stop attachment location onthe body.

The inserter instrument can include a scale. The scale can include aplurality of indicia on an outer surface of the body corresponding to orindicating different depths of insertion of the instrument.

The inserter instrument can further include an adjustable insertion stopattachable to the body, and preferably the scale part, at differentlongitudinal positions. The insertion stop can act to control the depthof insertion of the inserter instrument.

A second aspect of the invention provides a kit of parts. The kit ofparts can comprise an inserter instrument according to the first aspectof the invention and can include any preferred features thereof. The kitof parts can further comprise an impactor dimensioned for slidableengagement within the cavity. The impactor can have a longitudinallength greater than the length of the cavity.

The impactor can include a distal part in the form of a rod. The distalpart can have a free end. The impactor can include a proximal part. Theproximal part can be in the form of a rod. The impactor can include anintermediate part. The intermediate part can have a form visuallydistinguishable from the distal and/or proximal parts. The intermediatepart can have a form different to the form of the distal and/or proximalparts. The intermediate part can be in the form of a flat beam. Theintermediate part can be closer to the distal end than the proximal end.The proximal part can be longer than the distal part or the distal partand the intermediate part. The impactor can include a handle attached toa proximal end of the proximal part. The intermediate part can bearranged between the distal part and the proximal part.

The kit of parts can further comprise a deformable implant including areleasable attachment mechanism. The releasable attachment mechanism canbe arranged to co-operate with the attachment mechanism of the distalend of the inserter instrument.

A further aspect of the invention provides an assembly comprising theinserter instrument aspect of the invention, including any preferredfeatures thereof, and a deformable implant.

A further aspect of the invention can include a method of use of theinserter instrument to implant a deformable implant in a bone cavity ofa patient.

An embodiment of the invention will now be described in detail, by wayof example only, and with reference to the accompanying drawings, inwhich:

FIG. 1 shows a kit of parts according to the invention and including aninserter instrument according to the invention in a disassembled state;

FIG. 2 shows the inserter instrument and kit of parts shown in FIG. 1 inan assembled state;

FIG. 3 shows a magnified view of a distal end of the assembly shown inFIG. 2;

FIG. 4 shows a perspective exploded view of the inserter instrumentaccording to the invention;

FIG. 5 shows a plan view of the inserter instrument in an assembledstate;

FIG. 6 shows a side view of the inserter instrument in an assembledstate;

FIG. 7 shows a transverse cross sectional view along the line A-A′ ofFIG. 5;

FIG. 8 shows a schematic side view of the deformable implant;

FIG. 9 shows a schematic side view illustrating the general shape of thedeformable implant in its deployed and collapsed states; and

FIG. 10 shows a perspective view of an impactor instrument part of thekit of parts.

Like items in different Figures share common reference signs unlessindicated otherwise.

With reference to FIG. 1 there is shown an exploded view of an inserterinstrument 1 and an implant 2.

FIG. 2 shows the instrument 1 in an assembled state with the implant 2attached thereto forming an assembly according to an aspect of theinvention.

FIG. 3 shows a magnified, partial cross section view of a distal end ofthe assembly including a distal end of the instrument 1 and the implant2 attached thereto.

The inserter instrument 1 can be used to deform the implant 2 prior toinsertion into a previously prepared bone cavity. When inserted in thebone cavity, the instrument can further be used to allow the deformableimplant 2 to retain to its deployed state, as illustrated in FIGS. 1 to3, in order to provide structural support to the bone cavity.

FIG. 4 shows an exploded perspective view of the instrument 1 and FIGS.5, 6 and 7 show respective plan, side and transverse cross sectionalviews of the instrument 1 in an assembled state.

Instrument 1 includes a body 100 having a generally circular cylindricalform and including a distal 102 and proximal 104 end. A central,longitudinal cavity 106 extends between the proximal and distal ends ofthe body 100 such that the body has a generally tubular construction.The inner wall of the body 100 which defines longitudinal cavity 106 hasa smooth or precision surface finish, for example a honed or gun drilledsurface, in order to avoid potential blockage of the cavity 106 by bonegraft material during use. The distal end 102 of the tubular bodyincludes an internal thread 108 which forms parts of a releasableattachment mechanism for the implant 2. The proximal end 104 of the bodyincludes an external threaded portion 110 which forms a part of a guidemechanism described in greater detail below.

A hopper 112, for receiving bone graft material, is provided toward thedistal end of the body 100. The hopper includes sloped side walls 114defining an upper opening 113 and which taper toward a lower opening 116in communication with the longitudinal cavity of the main body 100.Hopper 112 extends in a direction substantially perpendicular to thelongitudinal axis of the main body 100. As best illustrated in FIG. 7,an undercut 115 is located at the junction of a forward end of theopening 116 and a lower part of a front wall 117 of the hopper 112. Theundercut 115 helps to avoid a user's fingers or gloved fingers frombeing trapped when feeding bone graft material through the opening intothe instrument.

A portion of the body distal to the hopper 112 includes a plurality ofmarkings or indicia, providing a scale. The scale 120 includes asubstantially planar surface portion bearing numbers and a correspondingplurality of markings extending circumferentially around the bodyindicating different potential depths of insertion of the instrument 1.

The instrument 1 also includes an instrument depth stop 122 generally inthe form of a clamp and having a pair of jaws 124, 126 connected by apivot 128 and a threaded knob 130 by which the stop 122 can be clampedabout the scale portion 120 of the body at different longitudinalpositions.

As mentioned above, a drive mechanism 132 is provided at a proximal end104 of the instrument 1. The drive mechanism 132 includes a cap 134including a barrel portion 136 bearing an internal thread 138dimensioned to cooperate with external thread 110. Cap 134 includes acavity therein within barrel section 136 and having an interior portion140 of greater diameter and presenting an end face or wall 140. Cap 134also includes a plurality of apertures, e.g. aperture 141, passingthrough the end wall which provide drain holes to facilitate cleaning ofthe end cap 134 after use. Cap 134 includes a plurality of recessedportions 142 disposed around the periphery of cap 134 and providing agrip formation for a user.

Instrument 1 also includes a push rod 150. Push rod 150 has a distal 152and proximal 154 end. As best illustrated in FIG. 7, push rod 150 isslidably received within the longitudinal cavity and extends therealong, and has a length greater than the length between the proximal anddistal ends of the main body 1. As illustrated in FIG. 7, the proximalend 154 of push rod 150 abuts against the inner face 140 of cap 132 andthe distal end 152 extends proud of the distal end 102 of the main body100. Toward the proximal end of the push rod 150, a pin 156 extends in agenerally downward direction from the push rod. Pin 156 is received in arecessed channel 158 fornled in the main body 1 toward its proximal end104. Channel 158 includes a closed end face against which pin 156 canabut to prevent further motion of the push rod in the distal direction.

An upper portion of body 100 includes a substantially flat surface 160extending from the distal end 102 of the body 100 up to the scale 120.The flat surface 160 is a discontinuity in the shape of the outersurface of the body 100 which otherwise has a circular cross section.The discontinuity formed by the flat surface portion creates a vent inuse which helps to prevent a seal being caused. This ensures that aircan be released during insertion and removal of the instrument, therebyreducing the risk of pressure building up, or a vacuum being formed,within the bone.

FIG. 8 shows a schematic side view of the deformable implant 2 ingreater detail. The construction of a suitable implant is described ingreater detail in WO 2010/097636 (International patent application no.PCT/GB2010/050337) which is incorporated herein by reference in itsentirety for all purposes.

FIG. 8 shows the stranded support structure implant 2 which can beimplanted in a cavity in a bone, to support the bone which defines thecavity. The implant has a spherical portion 4 which is rounded at afirst end 6 of the implant, and a cylindrical throat portion 8 at asecond end 10 of the implant.

The implant 2 is formed from twelve wires 12 which are formed from anickel titanium shape memory alloy which has been treated so that itexhibits enhanced elastic properties. The wires have a diameter of 0.5mm.

Each of the wires is formed into a loop 14. The loops are gatheredtogether at the first end 6 of the implant so that two lengths of eachwire extend from the first end. There are therefore 24 lengths of thewires extending from the first end of the implant, which are braided.The configuration of the spherical portion 4 is such that the implantflares outwardly from the first end 6 towards a wide point 16, andtapers inwardly from the wide point towards the throat portion 8.

The implant includes a retainer clip 18 at its first end which engagesthe twelve loops 14 formed in the wires 12 to control their spacing.

The implant includes a ring clamp 20. The ring clamp 20 comprises aninternal support ring 22 and an outer ring 24. The internal support ring22 is formed from stainless steel and defines a cylindrical supportsurface 26 which extends axially along the ring from a first end, up toa step 28. The internal support ring 22 has an externally threadedcollar 30 at its second end, beyond the step 28.

The outer ring 24 is formed from a nickel titanium based shape memoryalloy which is treated so that it can be heated to a temperature whichis above the characteristic A_(f) temperature of the alloy to cause thering to contract radially.

The implant 2 is generally similar to that described in WO 2010/097636,but the clip 18 differs in that it does not include a spigot or socketfeature but rather presents any plain surface with which the distal endof the push rod can engage in order to deform the implant as describedin greater detail below with reference to FIG. 9 in particular.

Operation of the inserter instrument will now be described withparticular reference to FIG. 9. FIG. 9 shows a schematic cross sectionaldiagram of the deformable implant 2 in its generally circular deployedstate 200 and also in its collapsed, insertion state 202. It will beappreciated that insertion state 202 is an approximation of the exactform adopted by the deformable implant for insertion. The exact formwill depend, on a variety of factors, including the stiffness of thewires of the cage, the deformation force applied and the action of theclip 18 on the wires defining the cage. However, as illustrated in FIG.9, in its deployed state 200, the implant has a generally wider andshorter form, than in its deformed, insertion state in which it isgenerally narrower and longer with respect to the longitudinal axis 204.

Prior to insertion of the deformable implant 2, a cavity is formed inthe patient's bone having a generally spherical form and beingapproximately 1 mm smaller in the diameter than the diameter of theimplant in its deployed state 200. This is to enhance the supportprovided by the implant and also the grip between the implant, whendeployed, and inner surface of the bone cavity. In order to preservebone stock, the cavity is created via a narrower channel through whichthe implant is inserted.

Initially, the implant 2 in its deployed state is attached to the distalend 102 of the insertion instrument 1 by engaging thread 30 into thread108 and screwing them together until resistance is felt. The implant 2is then slackened off by a quarter turn in order to facilitate eventualrelease of the implant 2 from the insertion instrument 1. The push rod150 is then introduced into the instrument 100 via the proximal end 104until the distal end 152 of the push rod engages the inner side of clip18, as best illustrated in FIG. 3. The cap 132 of the drive mechanism isthen threadingly engaged with thread 110 at the proximal end of theinstrument and rotated. Eventually, the inner wall 140 of cap 132 willabut the proximal end 154 of the push rod. Further rotation of cap 132will cause a driving force to be exerted on the push rod in the distaldirection causing deformation of the implant 2 by the action of distalend 152 of the push rod on the inner surface of clip 18. Hence, theimplant 2 will start to deform as illustrated in FIG. 9 by increasingits length and decreasing its transverse width. The cap 132 is rotatedby the user until the implant has deformed sufficiently to snugly fitwithin the access tunnel to the spherical bone cavity. Pin 156 andchannel 158 provide a push rod stop to prevent over extension of thepush rod. Pin 156 prevents the push rod 150 from extending too far inthe distal direction by engaging with the end face of channel 158thereby preventing further extension of the push rod in the distaldirection. Further, pin 156 in channel 158 prevents rotation of the pushrod about the longitudinal axis of the cavity and relative to the body100.

At some stage in the procedure, once the size of the deformable implant2 has been selected, the insertion stop 122 is clamped about the body100 at a scale position corresponding to the size of the attachedimplant. For example, different diameter implants can be provided. Thegreater the size of implant, the less the depth of insertion required bythe instrument. Therefore, by adjusting the position of the inserterstop clamp 126, the depth of insertion of the instrument can becontrolled. A guide tube (not shown) is provided into which the inserterinstrument 1 and implant 2 are inserted. A proximal part of the guidetube provides an abutting surface against which stop 122 can abut toprevent further insertion of the inserter instrument into the patient'sbone. Hence, inserter stop 126 helps to control the correct depth ofinsertion of the instrument to ensure that the implant is located at thecorrect depth in the cavity for deployment. The longitudinal position ofthe stop 122 along the longitudinal axis of the instrument 100 can beadjusted and the scale markings provide a visual guide to the user as tothe correct position to place the stop corresponding to the size ofimplant 2 being used.

Once the implant has been inserted to the correct depth, the cap 132 canbe rotated in the opposite direction through its drive rotationdirection and the spring force of the implant 2 pushes against thedistal end 152 of the push rod so as to urge the push rod 152 in theproximal direction. By continuing to unscrew cap 132, the cap 132 caneventually be removed from the instrument body 100 thereby exposing theproximal end 154 of the push rod. The push rod 150 can then be removedfrom the cavity of the body 100 while keeping the implant in position inthe bone cavity.

A mixture of graft material can then be introduced into hopper 112. Animpaction instrument 210 can then be used to drive bone graft materialinto the interior of the implant 2 within the bone cavity. Impactioninstrument 210 includes a handle 212 at a proximal end. A proximalportion 214 extends from handle 212 in the form of a rod. Intermediateportion 216, in the form of a generally planar thin beam extends fromproximal portion 214 to a distal portion 218 similarly in the form of acircular rod. The intermediate portion provides a visual indicator to auser to help prevent accidental removal of the impaction rod 210 duringbone graft impaction. When a user sees the change in diameter betweenproximal portion 214 and intermediate portion 216, then they should stopwithdrawal of the impaction rod 210 to ensure that it does not escapefrom the proximal end 104 of the instrument 100. The intermediateportion is positioned along the longitudinal axis of the impactioninstrument 210, such that it will be visible out of the proximal end ofthe instrument 100, when the distal end of the impaction instrument 210is adjacent the location of the hopper opening 116 so that bone graftmaterial can pass into the instrument for impaction by pushing theimpaction rod in the distal direction.

More specifically the length of distal portion 218 (between free end 219and junction 217) is substantially the same as the distance between theproximal end 104 end surface and a rear end of opening 116. Hence, whenjunction 217 is just visible to a user out of the end 104 of theinstrument, the distal end 219 will be just adjacent the rear end ofhopper opening 116 which will not be clear and no longer occluded by theimpaction instrument 210 at all. Hence, the user knows that theimpaction instrument does not need to be further withdrawn in order toadd bone graft. The distance between the distal end 219 and junction 215is substantially the same as the distance between the proximal end 104end surface and the forward end of opening 116. Hence, when junction 215is just visible to a user out of the end 104 of the instrument, thedistal end 219 will be adjacent the forward end of hopper opening 116which is just starting to be cleared with the impaction instrument 210in that position. Hence, the user knows that the impaction instrumentonly needs to be withdrawn a short further distance in order to fullyclear opening 116. Hence, the junctions 215, 217 provide visual feedbackto the user as to the position of the distal end 219 of the impactioninstrument relative to the hopper opening and the extent to which thehopper opening is clear to add more bone graft to the instrument.

As explained above, a proximal part of the guide tube provides anabutting surface against which stop 122 can abut to control the depth ofinsertion of the inserter instrument into the patient's bone. Duringimpaction of bone graft, the abutment of stop 122 against the guide tubealso helps to reduce the transfer of impaction forces to the implant 2thereby helping to avoid the position or shape of the implant form beingaffected. Hence, impaction forces created by the impaction instrument210 being used to drive bone graft material into the bone cavity arelargely transferred to the surface of the patient's bone by the actionof impactor handle 212 being transferred via stop 122 to the guide tubewhich itself engages the patient's bone rather than the implant 2.

Impaction instrument 210 is used to impact sufficient bone graftmaterial into the implant cavity as desired by the surgeon. In order toremove the insertion instrument 100, the insertion instrument is rotatedabout its longitudinal axis so as to unscrew implant 2 from the distalend 108 thread of the instrument 100. The frictional force between theimplant 2 and the bone cavity helps to retain the implant 2 within thebone cavity thereby allowing removal of the instrument while retainingthe implant in the bone cavity.

The instrument and parts thereof can be made from any suitable material,such as surgical grade stainless steel. Plastic materials can be usedfor the end cap 132, handle 212 and handle 130. Alternatively, metalcomponents throughout can be provided.

The push rod 150 can have a length of approximately 450 mm and adiameter of approximately 5 mm. The insertion instrument 100 can have alength of approximately 400 mm. The diameter of the implant can rangefrom approximately 18 mm to 26 mm in 2 mm increments.

As will be appreciated, the drive rod 150 is longer than the instrumentbody 100. As illustrated, the length of the drive rod 150 isapproximately the length of the guide body plus the length of theimplant 2 in its deformed state. The guide rod may be sufficiently longto encompass the full range of sizes of implant. Also, the guide rod ispreferably sufficiently long to include the size of the largest implant2 in its deformed state, the length of the instrument body and a slightexcess of length to abut the inner surface 140 of the cap 132 so as toprevent the cap binding against the threaded proximal end 104 ofinstrument 100. The use of a cap in the form of a rotatable knob andusing a threaded drive mechanism provides a particularly simple yeteffective drive mechanism. Further, the cap 132 can be removed from theinstrument to allow removal of the push rod 150 from the cavity therebyallowing the cavity also to be used to deliver bone graft material tothe implant. Hence, there is no need to introduce or attach a secondaryinstrument in order to deliver bone graft into the implant.

Various modifications and variations will be apparent to a person ofordinary skill in the art from the above teaching. For example, othertypes of drive mechanism which can abut the proximal free end of thepush rod to drive it distally may be provided.

The invention claimed is:
 1. A kit of parts for inserting a deformableimplant into a cavity in a bone of a patient, the kit of partscomprising: an inserter instrument comprising a body having a cavityextending along a longitudinal axis of the body from a distal end to aproximal end and including an attachment mechanism at the distal end towhich a deformable implant can be releasably attached, a drive mechanismat the proximal end of the body, and an insertion stop mounted on thebody and arranged to control the depth of insertion of the inserterinstrument into a guide tube; a push rod slidably arranged within thecavity and having a distal end engageable with a part of the deformableimplant and a proximal end abutable by the drive mechanism, wherein thedrive mechanism is operable to drive the push rod toward the distal endof the body; and an impactor dimensioned for slidable engagement withinthe cavity; wherein the stop comprises: a member extending from the pushrod; and a channel in an inner wall of the body having an end wall, andwherein the member is arranged to slide within the channel and to abutagainst the end wall.
 2. The kit of parts as claimed in claim 1, whereina part of the drive mechanism is removable from the instrument andwherein the push rod is slidably removable from the instrument via theproximal end of the body.
 3. The kit of parts as claimed in claim 1,wherein the push rod has longitudinal length greater than a longitudinallength of the cavity of the body.
 4. The kit of parts as claimed inclaim 1, wherein the drive mechanism includes an internal thread, anexternal thread co-operating with the internal thread and a cap, whereinthe cap is arranged to abut the proximal end of the push rod and the capincludes a one of the internal thread and the external thread and theproximal end of the body includes the other of the internal thread andthe external thread.
 5. The kit of parts as claimed in claim 4, whereinthe external thread is provided on an outer surface of the body at theproximal end of the body and the internal thread is provided on an innersurface of the cap.
 6. The kit of parts as claimed in claim 4, whereinthe cap includes a grip formation disposed around on an outer surfacearound its periphery providing a grip for rotation of the cap about thelongitudinal axis by a user.
 7. The kit of parts as claimed in claim 1,wherein the inserter instrument further comprises a hopper attached toan upper surface of the body and including a lower opening incommunication with the cavity.
 8. The kit of parts as claimed in claim1, wherein the inserter instrument further comprises a flat uppersurface extending along the body.
 9. The kit of parts as claimed inclaim 1 wherein the inserter instrument further comprises a scaleincluding plurality of indicia on an outer surface of the body andindicating different depths of insertion of the instrument.
 10. The kitof parts as claimed in claim 9, wherein the insertion stop is anadjustable insertion stop attachable to the scale at differentlongitudinal positions to control the depth of insertion of the inserterinstrument.
 11. A kit of parts as claimed in claim 1 wherein theimpactor has an impactor longitudinal length greater than the length ofthe cavity.
 12. The kit of parts as claimed in claim 11, wherein theimpactor includes a distal part in the form of a rod and having a freeend, an intermediate part in the form of a flat beam, a proximal part inthe form of a rod, a handle attached to a proximal end of the proximalpart and wherein the intermediate part is arranged between the distalpart and the proximal part.
 13. The kit of parts as claimed in claim 11or H, and further comprising: a deformable implant including areleasable attachment mechanism arranged to co-operate with theattachment mechanism of the distal end of the inserter instrument.